1. Field of the Invention
The present invention relates to a control method of a communication system, a communication controller, a control method of a data processing system, a communication system and programs. More specifically, the present invention relates to a technology, which is effective and can be adopted as a computer network technology, which executes packet transfer communication using communication protocols such as TCP/IP (Transmission Control Protocol)/(Internet Protocol).
2. Description of the Related Art
In the field of computer networks, physical media for high-speed networks have developed and have become increasingly popular year after year. Today, it is not exceptional for personal computers to comprise ports for Gigabit Ethernet, and a network adapter (hardware connected to the information processor for transferring data to networks) for use with 10-Gigabit Ethernet (Trademark) is available.
Although the physical media have developed supporting increased data rates, the processing speed of TCP/IP, the predominant protocol of use in computer networks, has not caught up with the transmission rates of the physical media. Even in an ultrahigh-speed network such as 10 Gbit Ethernet, the actual transmission rate of the information processor even with an extremely high-speed CPU cannot equal the speed of the physical media, which gives rise to the issue that it is not possible to fully utilize the communication capacity of the network. Technologies for addressing the issue of protocol processing and for speeding up communications have been much examined.
The technology for high-speed protocol processing currently prevalent is a technology called TCP segmentation offload. According to this technology, packets are transferred with a size larger than the maximum size (MTU) that can be transferred to a network when transferred from an information controller to a network adapter. Over-sized packets are divided into packets of a size which can be transferred to the network by the network adapter. By so doing, a transmitting information controller can generate packet headers in units of large data size, reducing the frequency of protocol processing for packet header generation. Consequently, it is possible for a CPU with low capacity to transfer a large quantity of data at high-speed.
This idea can be applied to the receiving end. That is, the loading of the protocol processing can be reduced in the information controller by assembling a large-sized packet from small-sized packets and transferring it to the information controller (as in Patent Document 1, for example).
This reassembly processing allows improvement of communication throughput (transferred data volume per unit of time), however because the information controller cannot start protocol processing during reassembly processing by the network adapter, an issue remains that communication delay time increases.
TCP segmentation offload is a method, which divides segments at the TCP level. Besides this method, there is an approach to reduce the loading of the host by dividing packets at the IP level. For example, Patent Document 2 describes a method to reduce the loading of the source and the destination information controllers by reassembly and fragmentation between Ethernet IP packets and the data in the high-speed bus of a communication server lying between the external Ethernet and the high-speed bus interconnecting servers instead of a network.
As explained above, the loading of protocol processing in an information controller can be reduced by accumulating the packets received via a network, reassembling the packets into a large packet and transferring the packet to the information controller. However, the accumulation of the received packets causes a delay in the arrival of the packet to the receiving information controller by the amount of time required for accumulation, thus causing an increase in delay time. The issue to be addressed is to control the increase in packet transfer delay time whilst maintaining the loading reduction effect by packet reassembly processing of the receiving information controller at the receiving end.    Patent Document 1: Japanese Published Unexamined Application No. 06-85822    Patent Document 2: Japanese Published Unexamined Application No. 2000-101613
It is an object of the present invention to provide a technology, which enables the simultaneous pursuit of reduction of loading in the host computer by the fragmentation and reassembly of the transmitted and received packets and reduction of transmission delay time of the transmitted and the received packets.
It is another object of the present invention to provide a technology, which allows the simultaneous pursuit of efficient utilization of the transmission rate of the information network by fragmentation and reassembly of the transmitted and the received packets and reduction in transmission delay time of the transmitted and the received packets.